BACKGROUND OF THE INVENTION
This invention relates to a tank lined with a metal lining, such as a carbon steel plate lining or a stainless steel plate lining, and a method for fabricating the same.
Recently, the metal lining of a tank is widely utilized in nuclear plants and chemical plants, but in the following description a tank lined with stainless steel plates for storing radioactive waste in a nuclear power plant will be described as an example.
In a nuclear power plant, a tank lined with stainless steel plates has been used for storing radioactive waste from the plant to decay the radioactivity of the waste. However, in these days, the capacity of a nuclear power plant has been enlarged, but the size of a housing of a nuclear reactor is limited in view of an accident such as earthquake. Therefore, it has been necessary to provide a tank having such capacity as can effectively store the radioactive waste and to promptly detect leakage of the stored radioactive waste at high sensitivities.
Generally, a lined tank of the kind mentioned above has been fabricated in the following manner.
Shaped steel members to be embedded in concrete are arranged in lattice form on a primary concrete floor slab and a secondary concrete slab is then filled on the primary concrete slab so as not to bury the upper surfaces of the embedded shaped steel members thereby forming the bottom of a tank. An inside and an outside molding frames for a side wall are fabricated with a space therebetween, which is thereafter filled with concrete, to form a lowermost stage of the tank. Pile-up working for forming a second stage, a third stage, .... on the lowermost stage are made subsequently. After the setting of the concrete, the molding frames are removed and lining plates are welded to the exposed portions of the embedded shaped steel members.
In such fabrication method, since respective stages are not assembled initially, but the stage is piled up one by one as occasion demands, the connecting portions therebetween may not often be arranged precisely so that, unnecessary strain or deformation may be applied to the lining plates. To accurately assemble respective stages by this fabrication method, more work, much time and additional apparatus are required.
Furthermore, it is necessary to carefully consider the problem as to the leakage of the radioactive waste through the weld seams of the lining plates which are formed to fabricate and construct a tank for storing concrete, and if the radioactive waste leaks through the weld seams, it flows through the small hole of the backing plate into the space and then flows downwards the space, during which the leakage is detected.
However, in this prior art device for detecting the leakage through the tank, since the space is essentially a blind structure in spite of the presence of the small hole of the backing plate, an operator cannot inspect the state of the device before the welding of the lining plates.